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Power Line Circuits
Last Updated on:
Friday, March 12, 2010 12:07 PM |
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| Circuits
Designed by Dave Johnson, P.E. : |
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ISOLATED AC CURRENT MONITOR
This circuit uses a small AC current transformer from Magnetek to produce an
isolated voltage proportional to the AC current in the primary winding.
The transformer contains a single turn primary with a low 0.001-ohm resistance.
It can easily handle 30 amps of AC current and provides at least 500vac of
isolation. With the components shown, the output AC voltage is scaled so 1
amp of current produces 100mv of AC voltage.
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UNPLUGGED POWER CORD ALARM
Many medical devices, such a portable X-ray and ultrasound equipment, carry
their own batteries. However, the frantic pace of some hospital emergency rooms
might cause the device to be shoved off into a corner without being plugged back
into an AC power source to recharge their batteries. So, I designed this circuit
to emit an audible alarm whenever the device’s power cord was unplugged from the
wall for a period of time. The device was designed to snap onto the outside of a
power cord, where it senses the AC electric field emitted. No direct connection
to the internal wires of the power cord is needed. I also included a low battery
voltage monitor.
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